ntag424 0.1.0

Implementation of the application protocol of NTAG 424 DNA chips.
Documentation 
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// SPDX-FileCopyrightText: 2026 Jannik Schürg
//
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

pub mod lrp;
pub mod originality;
#[cfg(feature = "sdm")]
pub mod sdm;
pub mod suite;

use subtle::ConstantTimeEq;

#[cfg(feature = "key-diversification")]
pub mod key_diversification;

/// Constant-time 8-byte equality for truncated MACs.
pub(crate) fn ct_eq_8(a: &[u8; 8], b: &[u8; 8]) -> bool {
    a.ct_eq(b).into()
}

/// Constant-time 16-byte equality for authentication nonces and full MACs.
pub(crate) fn ct_eq_16(a: &[u8; 16], b: &[u8; 16]) -> bool {
    a.ct_eq(b).into()
}

#[cfg(test)]
mod tests {
    use super::{ct_eq_8, ct_eq_16};

    #[test]
    fn ct_eq_8_accepts_equal_inputs() {
        assert!(ct_eq_8(b"12345678", b"12345678"));
    }

    #[test]
    fn ct_eq_8_rejects_first_byte_mismatch() {
        assert!(!ct_eq_8(b"02345678", b"12345678"));
    }

    #[test]
    fn ct_eq_8_rejects_last_byte_mismatch() {
        assert!(!ct_eq_8(b"12345670", b"12345678"));
    }

    #[test]
    fn ct_eq_16_accepts_equal_inputs() {
        assert!(ct_eq_16(b"1234567890abcdef", b"1234567890abcdef"));
    }

    #[test]
    fn ct_eq_16_rejects_first_byte_mismatch() {
        assert!(!ct_eq_16(b"0234567890abcdef", b"1234567890abcdef"));
    }

    #[test]
    fn ct_eq_16_rejects_last_byte_mismatch() {
        assert!(!ct_eq_16(b"1234567890abcdee", b"1234567890abcdef"));
    }
}